1. Field of the Invention
The present invention relates to a process for the sterile packaging of a prosthetic implant made of polyethylene.
The invention is particularly applicable to the packaging of high density polyethylene (HDPE) implants, particularly for knee or hip prostheses.
2. Brief Description of the Related Art
Between their manufacture and their implantation in a living being, such implants must be stored under good conditions of sterility, while allowing transport thereof. In order to sterilize these pieces which do not withstand high temperatures, it is known to use ionizing rays, particularly γ (gamma) rays. Moreover, in order to ensure that no subsequent contamination occurs, the implants are packed so as to be impermeable to the ambient air.
However, it is now known that, if polyethylene implants are exposed to radiation while the gaseous atmosphere surrounding the implants contains oxygen, phenomena of oxidation of the polyethylene occurs. More precisely the exposure to radiation provokes the break of polyethylene chains of the polyethylene which, in the presence of oxygen, recombine with the latter, leading to the reduction of the molecular weight of the polyethylene and to the degradation of its mechanical properties. In the absence of oxygen, polyethylene chains recombine together, increasing the rate of cross-linking of the polyethylene, which guarantees good mechanical properties of the implant.
This is the reason why one type of process presently employed consists in firstly placing an implant in a flexible, gas-impermeable sachet, then in creating a vacuum in this sachet before closing it hermetically, and finally in sterilizing the implant contained in the sachet in vacuo by exposure to radiation.
Nonetheless, the use of such a sachet in vacuo is delicate as it is difficult to guarantee the long-term integrity of the package, particularly during transport thereof. Any defect in the closure of the sachet or the presence of a weak or fragile area of the sachet will compromise the sterile packaging of the implant.
It is an object of the present invention to propose a process of the afore-mentioned type, in which a polyethylene implant is sterilized satisfactorily while guaranteeing a long-term sterile environment of the implant, particularly during transport thereof.